Most of the MG's in the US today were imported as DEWATs and reactivated during the 1968 amnesty. Prior to 1986, it was legal (though never easy) to import machineguns.
But the designation of a gun as a C&R, either by its being on the C&R list, or under the 50-year rule, doesn't mean that those guns are available. It only says that IF you have a legal, registered Model XYZ, it is a C&R.
I sold some WWII MGs to 03 licensees in adjacent states; after Form 4 approval, I simply put them in the trunk of the car and took them to the buyers' homes. (The Form 4 includes permission to take/ship the gun out of state; a separate form is not necessary.)